First Screen Testing for Birth Defects

I was given the option to have the First Screen test done at around 12 weeks.  This test is done while your pregnant, to determine if there is a greater risk of the baby having some birth defects such as Down syndrome and trisomy 18.  The assessment includes a blood test and a special ultrasound measurement called nuchal translucency.  The purpose of the blood test is to measure the proteins that are made by every developing baby and the placenta, and are found in every pregnant woman's blood.  If the fetus is at great risk for Downs syndrome or triomy 18 the levels of these proteins will be abnormal.  The nuchal translucency (NT) is a measuement of the fluid filled space in back of the fetus' neck. The fetus is at higher risk for certain birth defects when there is extra fluid present in this space.  This test does not provide a diagnosis it just predicts a greater chance of your baby having Down syndrome or trisomy 18.  These tests are only done in the first trimester.     

First trimester screening leads to the dection of approximately 83% of Down syndrome cases adn 80% of trisomy 18 cases.  It is a helpful test especially if the pregnant woman is 35 years old or older. 

Results of the test are affected by:

• How for along you are on the day the tests are performed.
• Your weight, ethnic background and again age.
• Whether you are an insulin-dependent diabetic or take certain types of medications.
• Whether a close relative has Down syndrome.

 Chorionic villi sampling (CVS)

CVS is an addition test that will be necessary if the First Screening test comes back abnornal.  This testing is done between 10 and 12 weeks of pregnancy.  A small amount of chorionic tissue (tissue from the developing placenta) is drawn for this test.  Chromosome analysis is done on the sample to determine any birth defects.  CVS is associated with a small risk of miscarriage.  Although I my Step Mother who had my sister while she was in her early 40's had this test done and she did not have a miscarriage and she had a healthy baby.

Amniocentesis

This test is preformed around the 16th week of pregnancy.  During this test a small amount of amniotic fluid is withdrawn from the uerus.  The fluid can then be tested for chromosome abnormalities, and also for open neural tube defects.  Amniocentesis can be risky though, a small risk of miscarriage is possible.  My friend had an amiocentesis and later miscarriaged.

Down syndrome

The risk of having a child with Down syndrome gradually increases with the age of the mother, but can occur at any age.  Down syndrome is caused by an extra chromosome (#21) and results in mental and physical abnormalities.  Approximately 1 in 800 babies are born with Down syndrome and it is the most common cause of mental retardation.

Trisomy 18

The risk of having a child with Trisomy 18 gradually increases with the age of the mother.  Trisomy 18 is also caused by an extra chromosome (#18) and results in serious mental retardation and physical deformities.  Major heart defects are possible as well.  Most babies born with Trisomy 18 do not live past the first year of their life.